1. Field of the Invention
The present invention relates to linear motors. More particularly, the present invention relates to linear motors that are suitable to be used for FA (factory automation).
2. Description of Related Art
A typical conventional linear motor has a mover 101 and a stator 102. Two linear guides 103 are mounted on the stator 102, and the mover 101 is mounted in a manner moveable along the stator 102, as shown in FIG. 16. A magnetic circuit is provided to generate a thrusting force to the mover 101. A surface 104 of the magnetic circuit opposing to the mover 101 is disposed between the two linear guides 103. In other words, the magnetic circuit has a single opposing surface 104, which is formed between the two linear guides. Also a variety of sensors 105 such as linear encoders and the like are disposed to detect the position of the mover 101. The sensors 105 are mounted on an exterior side surface of the linear motor or other exterior surfaces outside the linear motor.
However, in the linear motor described above, the opposing surface 104 of the magnetic circuit is formed between the two linear guides 103. As a result, a magnetic attraction force generated between the stator 102 and the mover 101 acts as a force that deforms the stator 102 and the mover 101, as shown by a two-dot and dash line shown in FIG. 16. Accordingly, the stator 102 and the mover 101 may need to be thicker or reinforced to secure a greater rigidity. This is an obstacle to designing a smaller and lighter linear motor. Also, since the magnetic circuit has a single opposing surface 104, it is difficult to obtain a high thrusting force.
Moreover, the various sensors 105 are mounted on an exterior side surface of the linear motor or other exterior surfaces outside the linear motor. As a result, plates that mounts the stator 102 and the mover 101 are bent by the magnetic attraction force described above, and therefore the gap distance in the various sensors 105 may substantially change. As a result, the position detection with a high precision becomes difficult, and dust and particles more likely affect the sensors. Moreover, the sensors become more vulnerable to mechanical external disturbances. For example, the sensors may likely contact objects that may come close to a moving path of the sensors.
It is an object of the present invention to provide a linear motor that increases the number of opposing surfaces of a magnetic circuit, and protects various sensors from mechanical external disturbances.
In accordance with one embodiment of the present invention, a linear motor has a linear guide and an armature-side block that are disposed inside a frame that linearly extends in its longitudinal direction, and opposing surfaces of a magnetic circuit can be formed at two locations that interpose the armature-side block. As a result, surfaces (opposing surfaces of a magnetic circuit) that generate a thrusting force of the linear motor are formed at two locations.
In accordance with one embodiment of the present invention, a linear guide and an armature-side block are disposed within a channel-shaped frame, and a linear encoder can be provided on or adjacent the linear guide. Accordingly, variations in the gap between the linear scale and the position detection sensor are difficult to take place when the linear motor is driven. In other words, the gap management is easy. Also, the linear encoder can be disposed in an area that is difficult to receive influences of leak magnetic fluxes of the main body of the linear motor, and thus a high accurate position detection can be conducted.
In accordance with one embodiment of the present invention, two linear guides are disposed on a frame and an armature-side block is mounted over the two linear guides. As a result, relative movements between the frame and the armature-side block are stabilized.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.